A rapid inflation rate is a requirement of many inflatable devices, particularly those used in an emergency, such as aircraft escape slides and inflatable rafts. In a typical inflation system a pressurized aspirating or pumping fluid is introduced as a high velocity stream or streams into a venturi nozzle adapted to discharge into the inflatable. The upstream end of the nozzle is open to the surrounding air during inflation and the high velocity gas stream, or streams, creates a suction to draw or aspirate ambient air into the stream or streams for increasing its or their volume. When the inflatable is substantially inflated, it is common practice to shut off or disable the aspirator and complete the inflation by use of the aspirating fluid alone.
A known aspirator includes an aspirator tube which is movable in and out relative to a housing that is fixed to the inflatable and mounts a group of jet tubes which convert the pressurized pumping fluid into high velocity jet streams. At the start of inflation the tube is extended into the inflatable to open an ambient air inlet at its outer end. Near the completion of inflation the aspirator tube is retracted out from the inflatable and its outer end functions as a closure for the ambient air inlet. Inflation is completed by the pressurized fluid alone. Such a prior art aspirator is shown by FIGS. 1 and 2. This type of aspirator includes a linear fluid motor that is connected to the aspirator tube by a connector rod. At the start of inflation some of the aspirating fluid pressure is directed into the linear fluid motor for moving the rod to extend the aspirator tube. A normally opened spool valve is provided in a passageway for delivering aspirating fluid pressure into the linear fluid motor. This valve is normally biased into an open position by a compression spring which is on one side of a movable wall. The opposite side of the movable wall is in communication with back pressure from the inflatable. When back pressure is developed this back pressure is imposed on the movable wall to produce a force in opposition the spring force. Near the completion of inflation the back pressure acting on the movable wall creates a force sufficient to overcome the force of the spring. When this happens the movable wall moves and repositions the valve spool to block flow of aspirating fluid into the linear fluid motor and at the same time vent the linear fluid motor. In response, a spring acts to retract the aspirator tube and close the ambient air inlet. A major disadvantage of this type of system is that the aspirator can only be set for a single pressure value, viz. a pressure sufficient to overcome the force of the biasing spring acting on the valve spool. An aspirator is required to operate over a large range of environmental conditions which have a direct effect on both pressure of the aspirating fluid at the inlet and back pressure in the inflatable. An aspirator set to close the ambient air inlet at a single pressure value is simply inadequate.
U.S. Pat. No. RE 27,860, granted Jan. 1, 1974, to Ronald H. Day, discloses an aspirator which operates in essentially the same way as the "prior art" aspirator shown by FIGS. 1 and 2 of the drawing. The aspirator tube retracts to close the ambient air inlet when the back pressure reaches a predetermined value and produces a force sufficient to overcome a spring force which biases the control valve into a first position.
U.S. Pat. No. 4,566,862, granted Jan. 28, 1986, to Richard A. Halavais, discloses an inflation system comprising a container of pressurized gas, a regulator for regulating the pressure of the gas as it leaves the container, a controller and an aspirator or ejector. The controller monitors the dynamic pressure within the aspirator and the static pressure within the inflatable to provide a feed back to the regulator. The objective is to provide a constant total mass flow through the aspirator at all times throughout the inflation cycle.
Other known inflation aspirators existing in the patent literature are shown by U.S. Pat. No. 3,460,746, granted Aug. 12, 1969, to Charles J. Green et al, by U.S. Pat. No. 3,460,747, granted Aug. 12, 1969, to Charles. J. Green et al, by U.S. Pat. No. 3,640,645, granted Feb. 8, 1972 to Alan K. Forsythe, and by U.S. Pat. No. 3,684,404 granted Aug. 15, 1972 to Lyle D. Galbraith.
A principal object of the present invention is to provide an improved inflation aspirator of the type having an aspirator tube which is retracted to close the ambient air inlet of the aspirator to, disable the aspirator, characterized by an improved control mechanism which causes such retraction to occur when the ratio of aspirating fluid pressure to back pressure approaches but has not yet reached a stall condition.